1. Field of the Invention
The present invention relates to a cutting method for substrates (for example, semiconductor wafers) in which a substrate is circularly cut by using a cutting blade and a groove is formed on a substrate by using it. The present invention relates to a cutting apparatus which is advantageously used for the cutting method.
2. Description of Related Art
Semiconductor devices (for example, semiconductor chips) are produced by the following processes. That is, a wafer (for example, a semiconductor wafer) which is composed of a semiconductor substrate material is prepared. Grid-like predetermined division lines are formed on a surface of the wafer, so that plural rectangular device regions are defined by the predetermined division lines on the surface of the wafer. Next, electronic circuits (for example, Integrated Circuits (=ICs) and Large Scale Integrations (=LSIs)) are formed on the device regions. Next, a rear surface of the wafer is ground, so that the wafer is thinned to have a desired thickness. Next, the wafer is divided along the predetermined division lines. As a result, the semiconductor devices (for example, semiconductor chips) are produced. In the above processes, in order to prevent the occurrence of damage (for example, cracking and breakage) in the wafer during handling of the wafer, a circumferential edge of the wafer may be chamfered before the thinning of the wafer.
When a wafer having a chamfered circumferential edge is thinned, the circumferential edge in a cross section is outwardly sharper and thinner so as to have a knife edge shape. Since the same damage may easily occur again in the above condition of the circumferential edge, the circumferential edge is subjected to cutting before thinning of the wafer so as not to have a knife edge shape, so that the circumferential edge has a surface which extends along a thickness direction of the wafer (which extends perpendicularly to a surface of the wafer) as disclosed in Japanese Unexamined Patent Application Publication No. 2000-173961. If damage (for example, cracking and breakage) occurs at the circumferential edge, the circumferential edge may be the origin of damage which extends to device regions having electronic circuits formed thereon, and the wafer itself may break and become unusable. Therefore, the above cutting of the circumferential edge is advantageous.
The cutting for preventing the generation of a knife edge shape is performed by forming either a ring-shaped step or a circular groove at a circumferential edge proximate to a surface of a chamfered wafer before thinning. The step and the groove have circular shapes which have diameters corresponding to a diameter of the wafer finally obtained and which have depths corresponding to a desired thickness of the wafer after thinning. When a rear surface of the wafer is thinned by grinding, the circumferential edge does not have a knife edge shape and has a surface extending along a thickness direction as disclosed in Japanese Unexamined Patent Application Publication No. 2000-173961 (in particular, FIGS. 2 to 4).
The above cutting of the circumferential edge uses the following method. That is, a wafer is held horizontally so that a surface thereof faces upward. A cutting blade, which is rotated at a high speed and is positioned above the wafer, is moved downward and cuts a layer of the wafer, which has a predetermined depth from the surface thereof, at a cutting start point on the wafer. From this condition, the wafer is rotated relatively to the cutting blade, thereby cutting the wafer in a horizontal direction.
In addition, in the field of semiconductor devices, there are cases in which either a wafer having a small diameter or a wafer having a shape different from a circular shape is obtained from a wafer having a relatively large diameter by cutting. In these cases, a cutting blade is moved downward and then cuts a layer, which has a predetermined depth from a surface of the wafer, in a horizontal direction as disclosed in Japanese Unexamined Patent Application Publication No. H11-54461.
In the cutting apparatuses disclosed in Japanese Unexamined Patent Application Publications described above, the wafer which is cut by the cutting blade is horizontally held on a disc-shaped rotation pedestal (for example, chuck table) by a device (for example, vacuum chucking device). The rotation pedestal has a rotation axis extending in a vertical direction. On the other hand, the cutting blade is coaxially provided at an end of a spindle having a rotation shaft. The spindle is supported such that an axial direction thereof horizontally extends in a radius direction of the chuck table. The cutting blade moves downwardly to the wafer and cuts it. While the cutting position of the cutting blade is secured, a groove or the like is circularly formed by rotating the wafer 1.
In the above cutting feature, since the circular cutting is performed while the cutting position of the cutting blade with respect to the wafer is unchangeable, two surfaces of the cutting blade are different from each other in wear amount. FIGS. 12A and 12B are schematic diagrams showing the above condition of the cutting blade. When a relative moving direction of a cutting blade 90 in an arrow direction curves at a predetermined rate, front and back edge portions (which correspond to a hatched portion in FIG. 12B) of the cutting blade 90 on an outer circumferential side of the moving direction strongly contact an internal wall surface of a groove 91 formed on the wafer 1. Due to this, an outer circumferential surface of the cutting blade 90 on the side of the moving direction wears more greatly than an internal circumferential surface thereof. When the wear amount of the one surface is larger than the other surface in the above manner, the wear occurs faster in this circular cutting method than in a typical linear cutting method, so that the lifetime of the cutting blade becomes short. As a result, the exchange frequency of the cutting blade is high, so that production is troublesome and production cost is high.